1. Field of the Invention
The present invention relates to a semiconductor memory device and a semiconductor memory card using the same.
2. Description of the Related Art
A semiconductor memory card having a built-in NAND-type flash memory is being miniaturized and provided with a high capacity rapidly. For example, an SD™ memory card is available in three card sizes such as an ordinary SD™ card size, a Mini SD™ card size and a Micro SD™ card size, and the Micro SD™ card is also demanded to have a high capacity. To realize a miniaturized memory card, it is being studied that the memory card is independently configured without housing it into a casing such as a base card, and such a card has been partly put in practical use.
A semiconductor memory card without a casing has external connection terminals formed on a surface of a wiring board by electrolytic plating or the like. Semiconductor elements such as a memory element and a controller element are stacked on the back surface of the wiring board. The semiconductor elements are electrically connected to the wiring board. The semiconductor elements mounted on the wiring board are sealed by a resin by mold forming. Such a semiconductor device is not housed into a casing but dependently used to configure a casing-free semiconductor memory card.
The casing-free semiconductor memory card is also demanded to be provided with a high storage capacity. Therefore, it is studied to mount plural memory elements on the wiring board by stacking on it. The size of the semiconductor memory card including its thickness is specified, so that it is necessary to decrease the thickness of each memory element to stack the memory elements into multiple layers. But, if the thickness of the memory elements is merely decreased, there is a possibility that the memory elements are cracked at the time of mold forming of the sealing resin because of an influence of the surface irregularities of the wiring board. Especially, there is a problem that the bottom memory element tends to be cracked among the multilayered memory elements.